Fantastic game I say. Jumping is weird, but other than that it's good. They totally had time into this.
I actually enjoyed this game as kid. It was always cool to see the little guy jummping for joy when he escaped the sinking sub. But why did the sub stay afloat when the game was over? You'd think that sub would be at the bottom of the ocean! :-) I will agree about the colision detection in Ben's comment. At times you could clear an obstacle, but at others (with what appeared to be an identical jump) you would get pulled back and not clear it. Still like it just for nostalgia's sake. (I got this game in the 80s from the bargain bin along with Bugs and Warplock.)
The object of the game was to try and escape from a sinking submarine. You begun the game in the bottom corner of the screen and had to work your way up the sub to reach the escape hatch at the top of the screen. You had to be quick for the water level was steadily rising and if you were too slow the game ended when you drowned.
As you made your way up the levels to the surface you had to collect keys (that were resembled by blocks) so as to be able to unlock the doors that would otherwise have prevented you from reaching the next level. Added to your problems was the small matter of rogue torpedoes that would be fired across the floor and you had to jump over them otherwise they would stun you and force you to lose time which often resulted in your man drowning. When the compartment flooded it did so instantly once the time limit was reached instead of gradually rising which made the game unnecessarily difficult.
There were some major flaws in this game, the biggest being that the collision detection was virtually non-existent for you could get stuck at any point in the game at any given time for any reason which added to the already high frustration level.